Constant-velocity universal joints are mounted at both end portions of a drive shaft which receives driving power from a differential gear of a vehicle. In this instance, the constant-velocity joints are means to equally transfer driving power of the differential gear even though the drive shaft does not keep a straight line. The constant joint serves to offset a change of velocity according to a refraction angle of the drive shaft using universal joint means with a great bending angle. A constant-velocity joint boot is combined to a driving part of the constant-velocity joint so that the driving part is sealed.
FIG. 1 is a perspective view showing an example that a boot 1 is applied to a constant-velocity joint (J). As shown in FIG. 1, a large-diameter tube body 2 of the boot 1 is combined to a driving part of the constant-velocity joint (J) so that a clamping band B1 pressurizes the outer peripheral surface of the large-diameter tube body 2 to maintain the combined state. A drive shaft (S) is combined to a small-diameter tube body 3 which is connected with the large-diameter tube body 2 through a bellows connection tube 4 so that a clamping band B2 pressurizes the outer peripheral surface of the small-diameter tube body 3 to maintain the combined state. Grease which provides a lubrication action is inserted into the constant-velocity joint boot 1 in order to improve driving performance of the driving part and to prevent invasion of foreign matters, such as dust or water, into the driving part of the constant-velocity joint (J) by the constant-velocity joint boot 1.
In the meantime, for the constant-velocity joints, there are rzeppa universal joints or bell type joints that a ball for transferring driving power is inserted into a ball retainer and a housing formed at one axis is combined with the ball retainer, and tripod joints that three pairs of rollers mounted inside a housing slidably move in an axial direction. A plurality of grooves which are formed in the axial direction are formed on the outer surface of the housing of the constant-velocity joint so as to make the constant-velocity joint lightweight, reduce required materials and enhance combining performance with the boot.
As shown in FIGS. 2 to 4, the constant-velocity joint boot 1 which are applicable to the rzeppa universal joints, the bell type joints or the tripod joints includes: a large-diameter tube body 2 combined with a housing of the constant-velocity joint; a small-diameter tube body 3 which accommodates the outer diameters of the large-diameter tube body 2 and the drive shaft; and a bellows connection tube 4 which connects the large-diameter tube body 2 and the small-diameter tube body 3 with each other, and the large-diameter tube body 2, the small-diameter tube body 3 and the bellows connection tube 4 are molded integrally. A combined member 5, which includes a thick protrusion part 5b combined to the groove formed in the housing of the constant-velocity joint and a thin protrusion part 5a accommodating the outer diameter of the housing of the constant-velocity joint, is mounted inside the large-diameter tube body 2.
The boot 1 in which the large-diameter tube body 2, the small-diameter tube body 3 and the bellows connection tube 4 for connecting the large-diameter tube body 2 and the small-diameter tube body 3 with each other are formed integrally is molded, and then, the combined member 5 which has the thick protrusion part 5b combined to the groove of the housing of the constant-velocity joint and the thin protrusion part 5a accommodating the outer diameter of the housing of the constant-velocity joint are combined is molded. After that, the combined member 5 is forcedly fit and adhered to the inside of the large-diameter tube body 2 of the boot 1 to be combined with the boot 1.
In such a case that the boot 1 and the combined member 5 are molded separately and assembled with each other, it deteriorates productivity because the number of processes is increased and it takes much time. Moreover, if the processes are not carried out accurately, because the boot 1 is not closely combined with the combined member 5, it may causes oil leakage during use.
Therefore, various methods and apparatuses for manufacturing a boot with excellent performance, which are reduced in the number of processes and process period of time, through a first molding step of integrally molding the large-diameter tube body 2, the small-diameter tube body 3 and the bellows body 4 for connecting the large-diameter tube body 2 and the small-diameter tube body 3 with each other and a second molding step of molding the combined member 5 inside the large-diameter tube body 2 of the first molded body in a double injection manner have been proposed and attempted.